It is standard in a large artillery piece, as for example the gun described in U.S. Pat. No. 2,756,635, for the firing-tube or barrel recoil to serve to slide open the breechblock and even extract the spent shell case, with the breechblock being latched in the open position. The breechblock is slid open against the force of a spring which is simultaneously loaded by the recoil force. The gunner chambers a new round and unlatches the breechblock which slides closed under the force of the loaded spring so the shot can be fired and a new cycle started. Such an arrangement can even be combined with an automatic recharging device.
At the start of firing it is necessary to manually open the breechblock and chamber a round, and it is occasionally necessary, as when a dud must be extracted, to have to manually close the breech. This operation is effected by a so-called charging handle connected via a crank of cam mechanism to the breechblock. The gunner must pivot this charging lever to slide the breechblock up, thereby opening the chamber and loading the recoil spring. Obviously the amount of force necessary to do this is considerable, since the lever simultaneously lifts the weight of the breechblock, overcomes the friction of the relatively massive mechanism, and loads the normally very stiff spring.
In order to ease this manual operation it is therefore standard to provide a relatively long charging handle. This maximizing of the lever arm does make operation simpler, but requires that quite some room be left free behind the piece. To overcome this problem it has been suggested to use a short lever connected to the breech-operating mechanism by stepdown gearing and a ratchet arrangement. Such a system is compact, but requires considerable ratcheting action, and the extra gearing increases losses in the manual actuator while adding to the complexity and bulk of the device.
It is also known, as for example from U.S. Pat. No. 3,362,292 to use a complex cam and latch arrangement in conjunction with a torsion-type leaf spring. Such a system can operate with a very short recoil stroke, but is so very complex that it adds greatly to the cost of the piece. The system has a plurality of cams and catches that rub on each other, creating considerable mechanical-energy losses that must be made up for by using a powerful recoil spring.